The present invention relates to an electroplating solution that can more efficiently and effectively deposit gold tin alloys, and to methods for providing such deposits.
Alloys of gold and tin, particularly in the compositional range of about 75 to 80 percent gold by weight, are useful as solders for the interconnection of electronic components. While gold-tin alloy solder materials are available as thermally processed performs, it is generally acknowledged that the ability to electroplate such materials allows the flexibility to deposit overall or in selected areas at will, and to adjust deposit thicknesses as required. For these reasons, much effort has been made to develop workable electroplating systems for these alloys, and numerous references are provided in the literature about such systems.
For many years, the trend in electronic device fabrication has been toward increasingly larger arrays and increasing complexity of such arrays. In practical electroplating terms, this means that at a given overall average current density, the local current density at the individual features of a component part in the array may deviate significantly from the average. Since in alloy plating systems the composition of the deposit is usually a function of current density, such deviations tend to limit the ability of the electroplating solution to deposit homogeneous films over large and complex arrays. For this reason, actual current densities employed in the fabrication of complex arrays tend to be rather low, and generally on the order of about 2-5 amperes per square foot.
It would be desirable to obtain electroplating solutions that are capable of depositing gold-tin alloy deposits as homogeneous films over current complex arrays. Accordingly, improved electroplating solutions are now provided by the present invention.